The present invention relates to low-speed, high-torque hydraulic devices, and more particularly, to such devices including a gerotor gear set including a stationary ring member and an orbiting and rotating star member.
Low-speed, high-torque gerotor motors are now routinely operated with pressure differentials (i.e., difference between inlet port pressure and outlet port pressure) of 2,000 to 3,000 psi. Some gerotor motors have recently been developed which are capable of operating continuously at pressure differentials even greater than 3,000 psi.
One of the primary causes of reduced volumetric efficiency in gerotor motors is leakage between each of the end surfaces of the gerotor star and the adjacent end surfaces of the housing or stationary valve member. Such leakage is inherent because the fixed ring member must be axially longer than the orbiting and rotating gerotor star, and because the adjacent housing surfaces are substantially parallel to each other, and are clamped to the end surfaces of the gerotor ring, there is an inherent clearance and leakage path along both ends of the gerotor star. Such leakage paths, and the resulting reduced volumetric efficiency, become even more significant as the operating pressure differential across the motor is continually being increased.